Simulations and experiments reveal unprecedented details about water motion in salt water – ScienceDaily

Simulations and experiments reveal unprecedented details about water motion in salt water – ScienceDaily

In salt water solutions, water molecules move rapidly around salt ions on a scale of more than a trillion times per second, according to both experiments and simulations led by scientists at New York University and the Sorbonne.

“There is more to salt solutions than meets the eye,” said Alexej Jerschow, a professor in NYU’s Department of Chemistry and one of the study’s senior authors. “This was evident when we measured and modeled the very fast dynamics of sodium chloride ions and the surrounding water molecules.”

The results, published in Nature Communicationit will allow researchers to build more reliable models for predicting ion dynamics, which could be used for a variety of scientific endeavors, from improving rechargeable batteries to MRIs.

Ions are ubiquitous and vital to life. Many ions, such as sodium and potassium, are pervasive throughout the human body and determine cell viability, nerve signaling, and the structural integrity of tissues. How ions interact with solvents also plays a critical role; for example, rechargeable batteries rely on the movement of ions through electrolyte solutions.

There are usually four to six water molecules surrounded by ions in a water-based solution, but how much these molecules move as a unit and how much motion the water molecules have is not well understood. Models used previously were inadequate to capture the concerted motion between water and the ions.

To study the movement of salt and water molecules, the researchers used nuclear magnetic resonance (NMR) spectroscopy, a versatile tool routinely used to determine the structure of molecules, and combined the experimental data with detailed computer simulations that can to model the dynamics around. salt ions on an atomic scale.

By testing salt water over a wide range of concentrations and temperatures, and combining experimental data and computer simulations, the researchers observed that water molecules move around the sodium and chloride ions at a very fast pace — more than a trillion once a second. Furthermore, it was previously assumed that ions move together with surrounding solvent molecules as a unit, but experiment has shown that this is not the case; instead, the water molecules wiggle much faster than the water-ion complex.

“​​​​We found excellent agreement between experiment and simulations, allowing us to build reliable models for ion dynamics,” said Jerschow.

“We are now turning to more complex electrolytes and what happens near solid surfaces, and combining experiments with simulations again will be crucial to progress,” said Benjamin Rotenberg of Sorbonne Université and France’s Center national de la recherche scientifique (CNRS), and another senior author of the study.

“We hope that this work can provide insights in many fields – from medicine to energy storage – that contribute to a better understanding of ion dynamics in solution,” said Jerschow.

The research was supported by the National Institutes of Health (R01EB026456), the European Research Council (863473), and the National Science Foundation (CHE2108205).

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